San Diego  A $10 million private donation may allow construction crews to break ground soon on a long-awaited library branch serving Hillcrest and Mission Hills, San Diego city officials said Tuesday.

The gift, which consists of $5 million from the Hervey family and $5 million from an anonymous donor, covers nearly half the cost of the $20.3 million project. The city is providing the rest of the money, primarily from infrastructure bonds.

The City Council unanimously agreed Tuesday to accept the donation and move forward with construction of the branch in late 2015 or early 2016. It's scheduled to open in late 2017 or early 2018.

Because $4 million of the city contribution comes from a bond issue that’s the subject of litigation, construction may be delayed until that money is available.

At 15,000 square feet, the new branch will be nearly four times the size of the 3,850-square-foot Mission Hills branch it’s replacing.

The new branch will be just north of Florence Elementary School on Washington Street between Front and Albatross streets — about four blocks east of the existing Mission Hills branch, which opened in 1961.

Council President Todd Gloria, whose district includes the site of the new branch, said he’s confident the project will be “beautiful” based on drawings he’s seen.

Public forums about the design will be held June 10 by the Hillcrest Town Council and June 12 by the Mission Hills Town Council, Gloria said.

Jay Hill, chief executive of the San Diego Library Foundation, credited Matthew Hervey for donating money from his family’s foundation and recruiting a second donor to match it.

“It’s really amazing and exciting,” Hill said.

The Hervey family also gave large donations to the $185 million Central Library, which opened downtown last September, and a branch in Point Loma that carries the family’s name.

The Mission Hills branch is one of 35 branches the city operates. Other branches slated for expansion and renovation include Skyline and San Carlos.